1. Field of the Invention
The present invention relates to a precision super-flat surface polishing technique capable of flattening a microstructure, such as a semiconductor device or a micro-machine. The present invention may be applied to polish steps in an optical structure formed of optical materials, such as calcium fluoride (CaF2), or a structural surface having defects. The present invention also relates to a super-flat surface polishing technique capable of rapidly and uniformly carrying out the chemical mechanical polishing (CMP) to an optional interface of such a microstructure or a laminated optical structure.
2. Background Art
FIG. 8 shows a conceptual perspective view for explaining a conventional chemical mechanical polishing machine. The chemical mechanical polishing machine carries out a chemical mechanical polishing process (CMP process) for flattening a surface or polishing up to an predetermined interface of a microstructure such as a semiconductor device or a micromachine, or of an optical structure made of an optical material, such as calcium fluoride (CaF2). Referring to FIG. 8, the chemical mechanical polishing machine holds a silicon wafer 85 on a head 83, and brings a surface of a silicon wafer 85 into contact with a pad 82 by a predetermined load 86, supplies a chemical liquid 84 containing abrasive grains at a predetermined flow rate onto a table 81 and rotates the head 83 and the table 81 for the chemical mechanical polishing of the silicon wafer 85.
From the industrial and functional point of view, the miniaturization of microstructures or optical structures has made a rapid progress in recent years and a design rule on the order of a value in the range of micrometers (xcexcm) to nanometers (nm) has been applied. Such chemical mechanical polishing techniques relevant to semiconductor fields are mentioned in xe2x80x9cThe National Technology Roadmap for Semiconductors Technology Needsxe2x80x9d, SIA, 1997 Edition.
FIG. 9 shows a cross sectional view of a semiconductor device for explaining a polishing process of an interlayer insulating film formed on a semiconductor wafer, and FIG. 10 shows a cross sectional view of another semiconductor device for explaining processes for flattening a metal film and forming buried wiring lines on a semiconductor wafer by chemical mechanical polishing. In a semiconductor device, as mentioned above, the wiring lines are densely arranged on the basis of a design rule on the order of a value in the range of micrometers to nanometers.
As shown in FIG. 9, a silicon dioxide film 93 is formed on a silicon wafer 94, and aluminum wiring lines 91 are formed on the silicon dioxide film 93. A silicon dioxide film 92 is formed on the silicon dioxide film 93 so as to cover the aluminum wiring lines 91. Under the situation, there has been a demand for a technique capable of flattening the surface of a silicon dioxide film 92 by removing a portion as indicated by xe2x80x9cPolished-offxe2x80x9d in FIG. 9 by chemical mechanical polishing.
Similarly, as shown in FIG. 10, a silicon dioxide film 103 is formed on a silicon wafer 104. A TiN/Ti film 101 and a tungsten CVD film 102 are formed by chemical vapor deposition process on the silicon dioxide film 103 to form buried wiring lines embedded in grooves of a silicon dioxide film 103. Under the situation, there has been a demand for super-flattening and high-speed polishing techniques to form buried wiring lines embedded in a silicon dioxide film 103 by subjecting the CVD tungsten film 102 and the TiN/Ti film 101 to chemical mechanical polishing.
Similarly, in micromachine fields, a processing technique is demanded which is capable of achieving processing in a high design rule higher than that demanded by the techniques relating to semiconductor devices. Similarly, in optical material fields, a processing technique is demanded which achieve an accuracy on an atomic level with respect to crystal plane orientation or crystal defects.
In a conventional flattening technique under the technical background as described above, a chemical mechanical polishing time (CMP time) has been calculated on the basis of a state after finishing chemical mechanical polishing, or a chemical mechanical polishing time has been calculated by using a measured film thickness determined by on-site observation. In a conventional technique for embedding a metal film, a chemical mechanical polishing time has been determined by monitoring a change in frictional force or vibration that occurs when the chemical mechanical polishing process changes from polishing a metal film to polishing an insulating film. For instance, as shown in FIG. 8, the changes of the rotational strain of the head 83 or the shaft of the table 81 are measured in a chemical mechanical polishing machine.
The conventional techniques, however, have the following problems. First, the silicon wafer 85 (See FIG. 8) that does not contribute to productivity is consumed, and time is wasted before starting production. When the pad 82 and the chemical liquid 84 are changed, the chemical mechanical polishing rate (CMP rate) changes accordingly. To know a removed amount and to stabilize the CMP rate, chemical mechanical polishing must be repeated, the chemical mechanical polishing condition must be examined, and the results of examination must be fed back to the chemical mechanical polishing process until a desired process condition is set.
Secondly, neither a fine change in polishing condition nor different polishing conditions distributed in the surface of the wafer can be easily corrected, and hence the accuracy of chemical mechanical polishing is reduced. An original signal indicating a rotational strain to which reference is made to know a chemical mechanical polishing condition is transferred through the head 83 and the table 81. Consequently, a signal is produced by averaging or deforming the original signal.
Accordingly, the present invention has been conceived to solve the foregoing problems and it is therefore an object of the present invention to provide a precision super-flat surface polishing machine and a precision super-flat surface polishing method capable of quickly and uniformly achieving the flattening of steps in a microstructure or an optical structure, or capable of achieving the flattening of the surface having defects of a structure. Further object of the present invention is to provide a precision polishing machine and a polishing method capable of controlling polishing up to a predetermined interface of a laminated structure of microstructures or optical structures.
According to one aspect of the present invention, a chemical mechanical polishing machine comprises at least two elastic wave sensors to be disposed so as to be in contact with a workpiece to be polished. The elastic wave sensors monitor elastic waves generated by chemical mechanical polishing rupture that occurs during a chemical mechanical polishing process for the workpiece. A means is provided for setting chemical mechanical polishing conditions to achieve uniform chemical mechanical polishing on the basis of signals provided by the elastic wave sensors.
According to another aspect of the present invention, a chemical mechanical polishing machine comprises an ultrasonic wave generator to be disposed so as to be in contact with a workpiece and capable of applying phonons to a part of the workpiece where lattice vibrations are generated. At least two elastic wave sensors are provided to be disposed so as to be in contact with the workpiece. The elastic wave sensors monitor phonon echoes generated by the part of the workpiece when the phonons are applied thereto during a chemical mechanical polishing process for polishing the workpiece. A means is provided for setting chemical mechanical polishing conditions for achieving uniform chemical mechanical polishing on the basis of signals provided by the elastic wave sensors.
According to another aspect of the present invention, a chemical mechanical polishing machine comprises an ultrasonic wave generator to be disposed so as to be in contact with a workpiece and capable of applying phonons to a part of the workpiece where lattice vibrations are generated. At least two elastic wave sensors are provided to be disposed so as to be in contact with the workpiece The elastic wave sensors monitor phonon echoes generated by the part of the workpiece when the phonons are applied thereto during a chemical mechanical polishing process for polishing the workpiece. A means is provided for setting chemical mechanical polishing conditions for achieving uniform chemical mechanical polishing on the basis of signals provided by the elastic wave sensors.
According to another aspect of the present invention, a chemical mechanical polishing machine comprises an ultrasonic wave generator to be disposed so as to be in contact with a laminated workpiece. The ultrasonic wave generator applies phonons to a part of the workpiece where lattice vibrations are generated during a chemical mechanical polishing process for the workpiece. At least two elastic wave sensors are provided to be disposed so as to be in contact with the workpiece. The elastic wave sensors monitor phonon echoes generated by the part of the workpiece. A means is provided for determining an end point of the chemical mechanical polishing process at an optional interface in the laminated workpiece on the basis of signals provided by the elastic wave sensors.
Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawing.